1. Field of the Invention
The present invention relates generally to air flow detectors and, more particularly, but not by way of limitation, to a detector system for detecting air infiltration leaks.
2. Brief Description of the Prior Art
The total air infiltration can be measured using rather sophisticated tracer gas techniques such as those discussed in an article entitled "A Prototype Semi-Automatic System For Measuring Air Infiltration In Buildings Using Sulphur Hexaflouride As a Tracer", C. M. Hunt and S. J. Treado, National Bureau of Standards, Technical Note No. 898 (1976). However, this test does not locate leaks which must be found by other methods. As the air flow velocity in an infiltration site may be into or out of the structure or building or may be zero depending on the ambient conditions, any technique to locate all of the air infiltration leaks generally will require a fan or blower to produce a unidirectional flow at all of the potential air infiltration leak sites. One technique to locate air infiltration leaks employs an IR imaging device, in conjunction with a large blower, to detect the temperature differences produced at the air infiltration leak site by the infiltrating air. This technique is fast and effective, but, requires a rather large capital investment. Another technique utilizes a sound source inside the building and a sound detector outside the building where an increase in sound level indicates a leak as described in Brookhaven National Laboratory Report 50952 (1978). Alternatively, a smoke generator can be employed inside a pressurized house to locate leaks by observing the efflux of smoke, "Retrofitting An Existing Wood-Frame Residence For Energy Conservation", D. M. Burch and C. M. Hunt, National Bureau of Standards Building Science Series No. 105 at page 71. While this last-mentioned system is inexpensive and simple to use, the smoke is slightly toxic and presents a health hazard for the operator.
In principle, it is possible to use a conventional, sensitive electronic anemometer or air motion detector to locate the influx of air through air infiltration sites produced by a blower. In practice, the motion of such an anemometer when used to scan the interior structure for infiltration sites creates a spurious air velocity in the anemometer which is typically larger than the velocity of the infiltrating air thereby rendering the instrument useless. It is one of the goals of this invention to eliminate the indication of such spurious signals by utilizing an electronic anemometer in a novel differential configuration.